EP 1,072,817 B1 discloses a hydro-mechanical transmission for an agricultural harvesting machine. Preferably, this is a combine harvester where the hydro-mechanical transmission drives the threshing rotor and enables a continuously variable speed adjustment of the threshing rotor. In this configuration, a clutch is driven by a drive engine. The clutch output is mechanically and drivingly connected to a hydraulic pump. The clutch output is further drivingly connected to a ring gear of a planetary gear set. In addition, the hydraulic pump is hydraulically connected to a hydraulic motor and drives the latter. The planet carrier of the planetary gear set is mechanically and drivably connected to the threshing rotor so as to drive it.
In order to provide a large conversion range the hydraulic pump is designed as a variable-displacement pump. The pump may be adjusted from a negative range of the displacement volume to a positive range of the displacement volume. If the hydraulic pump is operated in the negative range, the individual components of the drive assembly have to transmit idle power. The components need to be sized accordingly. In the hydro-mechanical transmission according to EP 1,072,817 B1, the clutch transmits the idle power so that it is capable of transmitting higher real amounts of power than the useful power.